Inflammatory and fibrotic disorders
Benign inflammatory changes of the mesentery often require careful differentiation from neoplastic processes.
- Mesenteric panniculitis. On CT, it visualizes as strand-like soft tissue changes encompassing the vessels without deforming them. A specific sign is the presence of the perivascular halo, which is a thin rim of normal adipose tissue surrounding the vessels.
- Sclerosing mesenteritis. Manifests as a fibro-adipose mass with irregular margins. Unlike panniculitis, fibrosis causes retraction of adjacent bowel loops and extensive calcification. Clinically, it may present as fever of unknown origin.
- Encapsulating peritoneal sclerosis. A chronic condition most commonly developing secondary to long-term peritoneal dialysis. CT reveals pronounced smooth or nodular peritoneal thickening with massive calcification. Bowel loops are tethered and thickened, and recurrent episodes of obstruction frequently occur.
Infectious processes and abscesses
Peritonitis and localized infections present with a variable imaging appearance depending on etiology and stage.
Peritoneal abscess goes through several stages. In the early stage, CT demonstrates a soft-tissue attenuation mass. As liquefactive necrosis progresses, a mature abscess forms with a well-defined, contrast-enhancing wall and a fluid center. The presence of gas within the walled-off cavity strongly points to an abscess, although this finding is not pathognomonic (also seen in necrotic tumors).
Tuberculous peritonitis has specific features:
- High-attenuation ascites (20–45 HU) due to high protein concentration.
- Smooth peritoneal thickening and a "smudged" omental pattern.
- Specific lymphadenopathy. Mesenteric lymph nodes feature a central area of low attenuation (due to caseous necrosis) with strong peripheral contrast enhancement. A similar nodal pattern occurs in Whipple's disease and certain metastases.
Peritoneal echinococcosis, caused by Echinococcus granulosus, typically occurs secondary to hepatic cyst rupture. CT demonstrates a multilocular cystic lesion with a characteristic calcified rim.
Mesenteric edema and vascular disorders
Adipose tissue edema is divided into systemic and local (most commonly ischemic).
In systemic diseases (heart failure, liver cirrhosis), edema is generalized. Tomograms show diffuse haziness of the mesenteric fat from the root of the mesentery to the bowel wall, accompanied by ascites and retroperitoneal edema.
In acute mesenteric ischemia, hypoxia increases capillary permeability. This leads to edema (increased X-ray attenuation of fat) and blood stasis in venules. Segmental mesenteric vessels are poorly visualized due to indistinct margins.
Tumors and tumor-like conditions
Most primary tumors of the mesentery and omentum require tissue verification, as their imaging appearance may mimic inflammation.
- Desmoid fibromatosis (mesenteric fibromatosis). A soft-tissue mass capable of causing segmental bowel ischemia due to vascular compression. Frequently associated with familial adenomatous polyposis.
- Cystic lymphangioma. A large benign lesion of the small bowel mesentery consisting of thin-walled cysts.
- Liposarcomas. Less common in the mesentery than in the retroperitoneum. Their appearance depends on the degree of differentiation. High-grade forms (pleomorphic, round cell) contain virtually no macroscopic fat. Large sarcomas often encase peripheral vessels in a sleeve-like manner.
- Epiploic appendagitis. Occurs due to torsion of the epiploic appendices. On CT, it appears as an oval fat-density lesion up to 5 cm in size. The condition is self-limiting, but clinically mimics appendicitis or diverticulitis.
For differential diagnosis: Panniculitis — vessels "float" within the halo without deformation; Sclerosing mesenteritis — tissues and bowel loops are "tethered" (retraction) and calcified.
Class and exam questions
Why do lymph nodes have central low attenuation in tuberculous peritonitis?
Central decreased attenuation is due to liquefactive or caseous necrosis. Meanwhile, the peripheral part actively enhances due to prominent vascularization of the inflammatory capsule.
Is gas within a fluid collection always a sign of a peritoneal abscess?
No. Although gas is typical for an abscess, this finding is not pathognomonic. It can also indicate a necrotic tumor or communication between the cavity and the bowel lumen.
How do malignant and benign omental lesions differ on CT?
Benign neoplasms are usually well-circumscribed. Malignant tumors have indistinct margins, infiltrate surrounding structures, and may be visually indistinguishable from inflammatory thickening.
What else to study on this topic
- Transmesenteric internal hernias and strangulated obstruction
- Differential diagnosis of mesenteric lymphadenitis and acute appendicitis
- MRI semiotics of cystic mesenteric lesions (T2 FS sequence)
- CT and MRI correlation in mesenteric liposarcomas
- The role of percutaneous fine-needle aspiration in the diagnosis of peritoneal abscesses
Master the entire topic in the "Diagnostic Radiology" course
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Other topics in the section "Diagnostic Radiology of the Abdominal Organs"
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